This invention relates to a variable force suspension system.
Known variable force suspension systems include variable force shock absorbers and/or struts that provide suspension-damping forces at a magnitude controllable in response to commands provided by a suspension system controller. Some systems provide control between two damping states and others provide continuously variable control of damping force.
In a known manner of control of a variable force suspension, the demand force for each variable force damper is determined responsive to a set of gains, the wheel vertical velocity and the body heave, roll and pitch velocities. An example system determines the body demand force as follows: DFb=GhHxe2x80x2+GrRxe2x80x2+GpPxe2x80x2, where DFb is the demand force, Gh is the heave gain, Gr is the roll gain, Gp is the pitch gain, Gw is the wheel velocity gain, Hxe2x80x2 is the body heave velocity, Rxe2x80x2 is the body roll velocity, and Pxe2x80x2 is the body pitch velocity. A control signal representing the determined body demand force is output to control the variable force damper responsive to the demand force. Example systems are described in U.S. Pat. Nos. 5,235,529; 5,096,219; 5,071,157; 5,062,657; 5,062,658; 5,570,289; 5,606,503; 5,579,229; 5,559,700; 5,510,988; and 5,570,288.
Modules are typically used by variable force damper systems for identifying and controlling different aspects of automotive control. The modules typically use specialized algorithms designed for interpreting the automobile""s input forces for a preferred control signal. In addition to the body control module described above, wheel and handling modules are also typically included in a complete suspension control system. One module known in the art commands individual damper outputs to a minimum damping state whenever the applicable desired force and damper wheel to body velocity signals are opposite in sign (a state in which the given damper is said to be in an xe2x80x9cactivexe2x80x9d quadrant). Within the limits of damper travel for small to medium-sized inputs, this approach provides acceptable vehicle body motion control. However, on larger inputs that cause the limits of damper travel to be tested, the absence of damping in the xe2x80x9cactivexe2x80x9d quadrants can allow very undesirable compression and/or rebound bumpstop impacts. In this context, compression and rebound bumpstops are defined as damper positions at which either full metal to metal impact and/or compression of one or more hard rubber parts occurs. To this end, wheel-to-body relative position-based xe2x80x9celectronic bumpstopxe2x80x9d algorithms have been used. Adversely, it has typically been difficult for the existing bumpstop algorithms known in the art to satisfactorily improve compression and/or rebound bumpstop impact energy without undesirable side effects on inputs that do not require the bumpstop algorithm use.
Therefore, it would be desirable to have an algorithm that would improve upon the above-mentioned situation, and related situations in which system control is released prematurely. Such an algorithm may provide superior gross motion control and reduced compression and/or rebound bumpstop activation during large events. Ideally, the algorithm would provide bumpstop and improved body motion control with minimal, if any, sacrifice in ride comfort and impact isolation.
The present invention is a method and system for controlling a vehicle suspension system. The method and system comprise determining a relative velocity between a wheel and a corresponding corner of the vehicle, and determining responsive to the relative velocity a raw wheel demand force. The method and system also comprise determining a relative position between the wheel and the corresponding corner of a vehicle body, determining a scale factor responsive to the relative position of the wheel, modifying the raw wheel demand force as a function of the scale factor to determine a scaled wheel demand force, and controlling the vehicle suspension system responsive to the scaled wheel demand force.
The features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiment, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.